Method for forming polyimide pattern using photosensitive polyimide and composition for use therein

ABSTRACT

This invention relates to a photosensitive polyimide material having positive-type or negative-type photosensitivity, which may be developed with a high resolution with an irradiation energy having short wavelength such as ultraviolet light or electron beam. The positive-type photosensitive polyimide composition comprising a solvent-soluble polyimide which shows positive-type photosensitivity in the presence of a photoacid generator, which is obtained by polycondensation of at least one aliphatic tetracarboxylic dianhydride and/or alicyclic tetracarboxylic dianhydride and at least one aliphatic diamine and/or alicyclic diamine and/or diaminosiloxane; and the photoacid generator. Since the polyimide has negative-type photosensitivity when irradiated with electron beam in the absence of a photoacid generator, a method for forming negative-type polyimide pattern using the polyimide is also provided.

This application is the national phase under 35 U.S.C. § 371 of PCTInternational Application No. PCT/JP00/03502 which has an Internationalfiling date of May 31, 2000, which designated the United States ofAmerica.

TECHNICAL FIELD

The present invention relates to a method for forming polyimide patternusing photosensitive polyimide and composition therefor. The presentinvention is useful for microscopic processing of semiconductors, thinfilm magnetic heads of hard disk drives and the like, and liquid crystaldisplays.

BACKGROUND ART

In production of various electronic parts including semiconductorintegrated circuits such as LSI, thin film magnetic heads of hard diskdrives and the like, and liquid crystal displays, very fine processingusing lithography is employed, and photoresists are widely used in theprocessing.

For electronic devices, not only high density and high performance, butalso large number of functions and high diversity are demanded, andphotoresist patterns with sizes of as small as less than 1 μm areformed.

Therefore, the light source used for irradiation is now being shiftedfrom g-line of mercury lamp (436 nm) to those having shorterwavelengths, that is, to i-line (365 nm) of mercury lamp, and further toKrF excimer laser (248 nm) and ArF excimer laser (193 nm).

Photoresist materials which are excellent in transparency to ultrashortwave, which have high sensitivity and high resolution, and which haveresistance to etching for microscopic processing have been proposed.

Aliphatic compounds such as acrylic esters and alicyclic compounds ofpolyvinylphenol, which have higher Tg than the conventional novolak typeresins have been proposed. However, a photoresist which may be used as astandard product, which satisfies the demands for positive-typephotoresist, such as good development by alkali, adhesion to substrateand resistance to dry etching, has not been available.

Polyimides are excellent in heat resistance, mechanical strength, andelectric insulation properties, and are recently applied to the field ofsemiconductors for which high reliability is demanded. Polyimides areapplied in semiconductors as passivation films, buffer coat films,α-ray-shielding films, interlayer insulation films and the like, andpositive-type photosensitive polyimides which can be developed with analkaline solution are now demanded rather than the conventionalnegative-type photosensitive polyimides.

Although it has been tried to give positive-type photosensitivity byconverting polyamic acid which is an unstable intermediate of polyimideto an ester derivative, the compound is poor in stability duringstorage, and a heat treatment at a temperature not lower than 350° C. isnecessary for imidation so that distortion is generated when thepolyimide is used for lamination of semiconductors (Y. Yamaoka et al.:J. Photopoly. Sci. Tech. Vol.9 293(1996)).

The present applicant previously developed a photosensitive polyimidecomposition and filed a patent application directed thereto(WO99/19771). This photosensitive polyimide composition comprises aphotoacid generator and a solvent-soluble polyimide which showspositive-type photosensitivity in the presence of the photoacidgenerator. This photosensitive polyimide composition is soluble in anorganic solvent, excels in adhesiveness, heat resistance, mechanicalproperties and in flexibility, and exhibits the properties of highlysensitive positive-type alkali-soluble photoresist upon irradiation withlight.

However, with the photosensitive polyimide composition disclosed inW099119771, satisfactory resolution is not necessarily attained when apattern with high resolution is to be formed by selectively exposing thepolyimide to a light having a short wavelength or electron beam.

DISCLOSURE OF THE INVENTION

Accordingly, an object of the present invention is to provide a methodfor forming thin film pattern of polyimide, by which a pattern having ahigh resolution may be formed by selective exposure with a light havinga short wavelength such as i-line (365 nm) of Hg-line, KrF excimer laser(248 nm) or ArF excimer laser (193 nm).

The present inventors intensively studied to discover that byselectively exposing the polyimide obtained by polycondensation betweenan aliphatic or alicyclic tetracarboxylic dianhydride and an aliphaticor alicyclic diamine or diaminosiloxane, which polyimide is notdisclosed in WO99/19771 to a light having a short wavelength or electronbeam, a pattern having high resolution may be formed, thereby completingthe present invention.

That is, the present invention provides a positive-type photosensitivepolyimide composition comprising a solvent-soluble polyimide which showspositive-type photosensitivity in the presence of a photoacid generator,which is obtained by polycondensation of at least one aliphatictetracarboxylic dianhydride and/or alicyclic tetracarboxylic dianhydrideand at least one aliphatic diamine and/or alicyclic diamine and/ordiaminosiloxane; and the photoacid generator. The present invention alsoprovides a method for forming a pattern of positive-type photosensitivepolyimide comprising the steps of forming a photosensitive layerconsisting essentially of polyimide composition according to the presentinvention on a substrate; selectively irradiating the photosensitivelayer with a light beam having a wavelength of not more than 365 nm;heat-treating the photosensitive layer; and developing thephotosensitive layer after the heat-treatment to selectively removeprescribed regions in the photosensitive layer. The present inventionalso provides a use of the polyimide of the present invention as amaterial for positive-type photolithography. The present inventionfurther provides a method for forming negative-type pattern of polyimidecomprising coating a substrate with the polyimide in the polyimidecomposition according to the present invention; selectively irradiatingthe polyimide with an actinic ray, the irradiated regions constituting adesired pattern; and developing the irradiated polyimide with analkaline solution to dissolve the non-irradiated regions. The presentinvention still further provides a use of the polyimide in the polyimidecomposition according to the present invention as a material fornegative-type photolithography.

By the method of the present invention, polyimide thin film patternshaving high resolution may be formed by selective exposure of thepolyimide thin film to a light having a short wavelength or electronbeam, such as i-line (365 nm) of Hg-line, KrF excimer laser (248 nm) orArF excimer laser (193 nm). The photosensitive polyimide used in themethod of the present invention is excellent in solubility in alkalinedeveloping solutions, and has sufficient resistance to dry etching.Further, the polyimide has excellent insulation performance and heatresistance. Therefore, the present invention is advantageous formicroscopic processing or the like of semiconductors, thin film magneticheads of hard disk drives, liquid crystal displays and the like.

BEST MODE FOR CARRYING OUT THE INVENTION

The polyimide used in the method of the present invention is asolvent-soluble polyimide which shows positive-type photosensitivity inthe presence of a photoacid generator, which is obtained bypolycondensation of at least one aliphatic tetracarboxylic dianhydrideand/or alicyclic tetracarboxylic dianhydride and at least one aliphaticdiamine and/or alicyclic diamine and/or diaminosiloxane.

The polyimide shows positive-type photosensitivity when irradiated witha light in the presence of a photoacid generator, and showsnegative-photosensitivity when irradiated with an electron beam in theabsence of a photoacid generator (although it shows negative-typephotosensitivity even in the presence of the photoacid generator).

The term “aliphatic tetracarboxylic dianhydride” means thetetracarboxylic dianhydride in which the moiety constituting the mainchain of the polyimide consists of an aliphatic structure, and thenumber of carbon atoms constituting the aliphatic structure ispreferably 1 to 15. The aliphatic structure may be either linear orbranched, and may contain (an) oxygen atom(s) (ether, ketone or thelike) and/or (a) nitrogen atom(s) (secondary, tertiary or quaternaryamine or the like) and/or (a) sulfur atom(s) (sulfide, disulfide,thioether, thiocarbonyl or the like). Thus, the term “aliphatic” as usedin the specification and claims also include those containing such (a)heteroatom(s) (this definition is also applied to the term “aliphaticdiamine”). The number of the heteroatom(s) is preferably about 1 to 3.The aliphatic structure is preferably a saturated aliphatic structure.Although other structures which do not adversely affect the advantageousfeature of the present invention may exist in the side chains, thetetracarboxylic dianhydride, including the side chains, most preferablyconsists of an aliphatic structure (with the proviso that theabove-mentioned oxygen atom(s) and/or nitrogen atom(s) and/or sulfuratom(s) may be contained) and/or alicyclic structure (with the provisothat the above-mentioned oxygen atom(s) and/or nitrogen atom(s) and/orsulfur atom(s) may be contained).

The term “alicyclic tetracarboxylic dianhydride” means thetetracarboxylic dianhydride in which the moiety constituting the mainchain of the polyimide consists of an alicyclic hydrocarbon, and thenumber of carbon atoms in the alicyclic moiety is preferably 3 to 20.The alicyclic moiety may contain (an) oxygen atom(s) (ether, ketone orthe like) and/or (a) nitrogen atom(s) (secondary, tertiary or quaternaryamine or the like) and/or (a) sulfur atom(s) (sulfide, disulfide,thioether, thiocarbonyl or the like). Thus, the term “alicyclic” as usedin the specification and claims also include those containing such (a)heteroatom(s) (this definition is also applied to the term “alicyclicdiamine”). In cases where the alicyclic moiety contains theheteroatom(s), the alicyclic moiety is heterocyclic. The number of theheteroatom(s) is preferably about 1 to 3. The alicyclic moiety ispreferably a saturated alicyclic moiety, especially saturated alicyclicmoiety containing 4 to 8 carbon atoms. The moiety constituting the mainchain of the polyimide is preferably one consisting of the alicyclicstructure and/or the above-mentioned aliphatic structure (with theproviso that the above-mentioned oxygen atom(s) and/or nitrogen atom(s)and/or sulfur atom(s) may be contained). Although other structures whichdo not adversely affect the advantageous feature of the presentinvention may exist in the side chains, the tetracarboxylic dianhydride,including the side chains, most preferably consists of an alicyclicstructure (with the proviso that the above-mentioned oxygen atom(s)and/or nitrogen atom(s) and/or sulfur atom(s) may be contained) and/orthe above-mentioned alicyclic structure (with the proviso that theabove-mentioned oxygen atom(s) and/or nitrogen atom(s) and/or sulfuratom(s) may be contained) and/or the siloxane structure described below.

The tetracarboxylic dianhydrides in which the moiety constituting themain chain of the polyimide consists of a structure having an alicyclicring to which an aliphatic group is bound may also preferably beemployed. In this case, as the alicyclic structure and as the aliphaticgroup, those described above, respectively, are preferred. Thus, thepolyimides in which the moiety constituting the main chain consists ofthe alicyclic structure and the aliphatic structure are also included in“alicyclic” in this specification and claims (this definition is alsoapplied to diamines”).

Preferred examples of the tetracarboxylic dianhydride (described in theform of monomers) constituting the polyimide include saturated alicyclictetracarboxylic dianhydrides,bicyclo(2,2,2)-oct-7-ene-2,3,5,6-tetracarboxylic dianhydride and5-(2,5-dioxo-tetrafurfuryl)-3-methyl-4-cyclohexene-1,2-dicarboxylicdianhydride. These may be employed individually or in combination.

The above-described tetracarboxylic dianhydride may be employedindividually or in combination.

Especially preferred examples of the tetracarboxylic dianhydride(described in the form of monomers) constituting the polyimide used inthe present invention include saturated alicyclic tetracarboxylicdianhydrides, particularly cyclopentanetetracarboxylic dianhydride,cyclohexanetetracarboxylic dianhydride and cyclobutanetetracarboxylicdianhydride. These may be employed individually or in combination. Sincethese compounds do not contain a double bond in the molecule, they arehighly transparent to ultraviolet radiation having extremely shortwavelength, and give high sensitivity and high resolution aspositive-type photoresist materials.

The term “aliphatic diamine” constituting the polyimide used in themethod of the present invention means the diamine in which the moietyconstituting the main chain of the polyimide consists of an aliphaticstructure, and the number of carbon atoms constituting the aliphaticstructure is preferably 1 to 15. The aliphatic structure may be eitherlinear or branched, and may contain (an) oxygen atom(s) (ether, ketoneor the like) and/or (a) nitrogen atom(s) (primary, secondary, tertiaryor quatemary amine or the like). The number of the heteroatom(s) (otherthan the two nitrogen atoms inevitably contained to constitute diamine)is preferably about 1 to 3. Although other structures which do notadversely affect the advantageous feature of the present invention mayexist in the side chains, the diamine, including the side chains, mostpreferably consists of an aliphatic structure (with the proviso that theabove-mentioned oxygen atom(s) and/or nitrogen atom(s) and/or sulfuratom(s) may be contained) and/or the below-described alicyclic structure(with the proviso that the above-mentioned oxygen atom(s) and/ornitrogen atom(s) and/or sulfur atom(s) may be contained) and/or thesiloxane structure described below.

The term “alicyclic diamine” means the diamine in which the moietyconstituting the main chain of the polyimide consists of an alicyclichydrocarbon, and the number of carbon atoms in the alicyclic moiety ispreferably 3 to 15. The alicyclic moiety may contain (an) oxygen atom(s)(ether, ketone or the like) and/or (a) nitrogen atom(s) (primary,secondary, tertiary or quaternary amine or the like) and/or (a) sulfuratom(s) (sulfide, disulfide, thioether, thiocarbonyl or the like). Incases where the alicyclic moiety contains the heteroatom(s), thealicyclic moiety is heterocyclic. The number of the heteroatom(s) (otherthan the two nitrogen atoms inevitably contained to constitute diamine)is preferably about 1 to 6. The alicyclic moiety is preferably asaturated alicyclic moiety, especially saturated alicyclic moietycontaining 4 to 8 carbon atoms. Although other structures which do notadversely affect the advantageous feature of the present invention mayexist in the side chains, the diamine, including the side chains, mostpreferably consists of an alicyclic structure (with the proviso that theabove-mentioned oxygen atom(s) and/or nitrogen atom(s) and/or sulfuratom(s) may be contained) and/or the above-mentioned alicyclic structure(with the proviso that the above-mentioned oxygen atom(s) and/ornitrogen atom(s) and/or sulfur atom(s) may be contained) and/or thesiloxane structure described below. As described in the explanation ofthe tetracarboxylic dianhydride, the term “alicyclic” include thosewherein the moiety constituting the main chain consists of an alicyclicring on which an aliphatic group is bound.

The term “diaminosiloxane” constituting the polyimide used in the methodof the present invention means the diamine in which the moietyconstituting the main chain consists of siloxane structure. The numberof silicon atom(s) is preferably about 1 to 50. Each silicon atom in thesiloxane structure may be substituted with one or more lower(C₁-C₆)alkyl group and/or lower (C₁-C₆)alkoxy group. In addition to thesiloxane structure, the diaminosiloxane may contain the above-mentionedaliphatic moiety and/or alicyclic moiety, and other structures which donot adversely affect the advantageous feature of the present invention,especially in side chains.

The above-mentioned diamine may be employed individually or incombination.

Preferred examples of the diamine (described in the form of monomers)used in the present invention include 1,3-bis(3-aminomethyl)cyclohexane,4,4′-diamino-dicyclohexyl-methane, bis(2-aminoethoxy)ethane,N,N-bis(3-aminopropyl)methylamine, ethylenediamine,2,2′-diaminodiethyldisulfide, 1,4-bis(3-aminopropyl)piperazine,3,4bis(3-aminopropyl)2,4,8,10-tetraoxa[5,5]undecane, diaminosiloxane,trans-1,4-diaminocyclohexane, 1,3-diamino-2-hydroxypropane and3(4),8(9)-bis(aminoethyl)tricyclo[5,2,1,0]decane. These may be employedindividually or in combination.

Other preferred examples of the diamine (described in the form ofmonomers) used in the method of the present invention includediaminosiloxanes such as 1,3-bis(3-aninopropyl)tetramethyldisiloxane(molecular weight: 248.5) and diaminosiloxane having amino groups atboth ends (amine value: 300-500), and the aliphatic polyimides usingthese diaminosiloxanes have good adhesion to semiconductor substrates.

In cases where the above-mentioned aliphatic or alicyclic diarnine ordiaminosiloxane contains disulfide moiety, since the disulfide reactswith an acid to easily become thiol, images are formed with highsensitivity and high resolution. Preferred examples of the diaminecontaining disulfide moiety include diarninodialkyldisulfides containingC_(1-C) ₆ alkyl group, such as diaminodiethyldisulfide.

Especially preferred aliphatic diamine used in the method of the presentinvention are aliphatic disulfides and/or diaminosiloxanes, and thepolyimides containing these form images with high sensitivity and highresolution.

The polyimide contained in the composition of the present invention issolvent soluble. Here, the term “solvent soluble” means that thepolyimide is dissolved in N-methyl-2-pyrrolidone (NMP) to aconcentration of not less than 5% by weight, preferably not less than10% by weight.

The weight average molecular weight of the polyimide contained in thecomposition according to the present invention is preferably 5000 to100,000, more preferably 5000 to 50,000. If the weight average molecularweight is 5000 to 100,000, good solvent solubility, membrane-formingproperty, membrane strength and insulation performance may be obtained.

The polyimide used in the method of the present invention may preferablybe synthesized by mixing the above-mentioned tetracarboxylic dianhydrideand the above-mentioned diamine at molar ratio of 1:(0.95-1.05) in anorganic solvent and heating the mixture in the presence of an acidcatalyst at 140-200° C., preferably at 150-180° C. The generated wateris eliminated from the reaction system by azeotropic distillation withtoluene, xylene, decalin or the like.

The polyimide used in the method of the present invention may beproduced by a process using the catalyst system utilizing the followingequilibrium reaction between a lactone, base and water.

{lactone}+{base}+{water}={acid}⁺{base}⁻

A polyimide solution may be obtained by using the {acid}⁺{base}⁻ systemas a catalyst and heating the reaction mixture at 140° C. to 180° C. Thewater produced by the imidation reaction is eliminated from the reactionsystem by azeotropic distillation with toluene. When the imidation inthe reaction system is completed, {acid}⁺{base}⁻ is converted to thelactone and the base, and they lose the catalytic activity and areremoved from the reaction system with the toluene. The polyimidesolution produced by this process can be industrially used as it is as apolyimide solution with high purity because the above-mentionedcatalytic substances are not contained in the polyimide solution afterthe reaction.

Examples of the reaction solvent which may be used in theabove-mentioned imidation reaction include, in addition to theabove-mentioned toluene, polar organic solvents. Examples of theseorganic solvents include N-methyl-2-pyrrolidone, dimethylformamide,dimethylacetamide, dimethylsulfoxide, sulfolane and tetramethylurea.

As the lactone, γ-valerolactone is preferred. As the base, pyridineand/or methylmorpholine is(are) preferred.

The mixing ratio (acid/diamine) between the tetracarboxylic dianhydrideand the diamine subjected to the imidation reaction is preferably about1.05 to 0.95 in terms of molar ratio. Further, the concentration of theacid dianhydride based on the total reaction mixture is preferably about4 to 16% by weight, the concentration of the lactone is preferably about0.2 to 0.6% by weight, the concentration of the base is preferably about0.3 to 0.9% by weight, and the concentration of the toluene ispreferably about 6 to 15% by weight at the initiation of the reaction.The reaction time is not restricted and varies depending on themolecular weight of the polyimide to be produced and the like, andusually about 2 to 10 hours. It is preferred to carry out the reactionunder stirring.

It should be noted that the production process per se of the polyimideusing the binary catalytic system comprising the lactone and the base isknown, and described in, for example, U.S. Pat. No. 5,502,143.

Examples of diluents include ketone solvents such as acetone,cyclohexane, methyl ethyl ketone and methyl isobutyl ketone; cellosolvesolvents such as methyl cellosolve, methyl cellosolve acetate, ethylcellosolve acetate and butyl cellosolve acetate; ester solvents such asethyl acetate, butyl acetate, isoamyl acetate, γ-butyrolactone andmethyl 3-methoxypropionate; and cyclic ether compounds such as dioxaneand dioxolan.

Further, propionic acid derivatives such as methyl methylpropionate;lactates such as ethyl lactate; and propylene glycol monomethyletheracetate, which draw attention as low toxic solvents in recent years, mayalso be used.

The above-mentioned solvents may be used individually or in combination.An aliphatic alcohol such as isopropyl alcohol may be added to thesesolvents in an appropriate amount.

Although the polyimide used in the method of the present invention maybe composed of one tetracarboxylic dianhydride and one diamine, by usingnot less than two components as at least one of the tetracarboxylicdianhydride and the diamine so as to form a copolymer containing totallynot less than 3 components, desired properties such as lighttransmittance, high resolution, adhesion with substrate, developingproperties by alkalis, and resistance to dry etching may be given. Inthis case, with a random copolymer, it is difficult to arbitrarilycontrol the properties of the polyimide produced, so that it is usuallydifficult to improve the properties of the polyimide. In general,improvement of properties of the polyimide is carried out by blockcopolymerization.

By carrying out the above-described imidation reaction sequentially intwo steps using different acid dianhydrides and/or different diamines,polyimide block copolymers can be produced. By the conventional processfor producing polyimide through polyamic acid, only random copolymerscan be produced as copolymers. Since polyimide block copolymers can beproduced selecting arbitrary acids and/or diamines, desired propertiesor functions as mentioned above can be given to the polyimide. In themethod of the present invention, such a polyimide copolymer maypreferably be employed.

A preferred process for producing the polyimide block copolymers includethe process wherein a polyimide oligomer is produced using the acidcatalyst generated by the above-described lactone and the base, andusing either one of the aromatic diamine component or thetetracarboxylic dianhydride in excess, and then the aromatic diamineand/or the tetracarboxylic dianhydride is(are) added (the molar ratio ofthe total aromatic diamines to the total tetracarboxylic dianhydride is1.05 to 0.95), thereby carrying out two-step polycondensation.

Polyimide block copolymers containing (an) alicyclic tetracarboxylicdianhydride(s), diaminosiloxane(s) and (an) aliphatic disulfide(s) maybe used as materials for photolithography giving a resolution of lessthan 1 μm.

To give high and precise resolution to the polyimide block copolymer,the block copolymer may preferably be an amorphous aliphatic oralicyclic polyimide block copolymer containing (a) group(s) havingdistortion, such as spiro ring group, in addition to the above-mentionedcomponent, thereby accelerating photodegradation of the polyimide.

To promote the transparency to a light having a short wavelength or toelectron beam, the polyimide used in the method of the present inventionpreferably does not substantially contain conjugated double bond and anaromatic structure. The term “does not substantially contain” means thatthe amount of the conjugated double bond and the aromatic structure isin a degree at which the object of the present invention, that is, toform a pattern with a high resolution, is not adversely affected.Usually, the amount(s) of the monomer(s) having conjugated double bondor aromatic structure is preferably not more than 10 mol %, morepreferably not more than 5 mol %, and most preferably 0 mol % based onthe total polyimide.

The polyimide used in the method of the present invention may contain(a) phenolic hydroxyl group(s), carboxyl group(s), thiophenol group(s)or sulfonate group(s), or (a) group(s) derived from these groups whichyield these groups by the above-mentioned photoacid generator. However,unlike the conventional photosensitive polyimides, the polyimide showsphotosensitivity even without these groups when a suitable developingsolution is used.

In cases where the above-described polyimide is used as a positive-typephotosensitive polyimide, a photoacid generator is used together. Theterm “photoacid generator” herein means a compound which generates anacid upon irradiation with light or electronic beam. Since the polyimideis decomposed by the action of the acid and is made soluble in alkalis,the photoacid generator employed in the present invention is notrestricted and any compound which generates an acid upon irradiationwith light or electron beam may be employed. Preferred examples of thephotoacid generator include onium salts having naphthalene skeleton orbenzothiophene skeleton, and sulfonate, sulfonyl and sulfamidecompounds.

Preferred examples of the photosensitive quinone diazide compoundsinclude esters of 1,2-naphthoquinone-2-diazide-5-sulfonic acid and1,2-naphthoquinone-2-diazide-4-sulfonic acid, the counterparts of theesters being low molecular aromatic hydroxyl compounds such as2,3,4-trihydroxybenzophenone, 1,3,5-trihydroxybenzene, 2-methylphenol,4methylphenol and 4,4′-hydroxy-propane.

Preferred examples of the onium salts which may be used as the photoacidgenerator include aryl diazonium salts such as 4(N-phenyl)aminophenyldiazonium salt; diaryl halonium salts such as diphenyl iodonium salt;triphenyl sulfonium salts such as bis{4-(diphenylsulfonio)phenyl}sulfide, and bis-hexafluoroantimonate.

It is preferred to add the photoacid generator in an amount of 5 to 50%by weight based on the weight of the polyimide resin component. In caseswhere the thickness of the polyimide membrane formed on a substrate issmall, it is usually preferred to use a small amount, within the rangementioned above, of the photoacid generator.

The photosensitive polyimide composition according to the presentinvention may be in the form of a solution suited for application onsubstrates. In this case, as the solvent, a polar solvent such asN-methyl-2-pyrrolidone, dimethylformamide, dimethylacetamide,dimethylsulfoxide, sulfolane, tetramethylurea or the like, which is usedas the solvent for the imidation reaction, may be employed. Theconcentration of the polyimide in the solution may preferably be 5% to50% by weight, more preferably 10% to 40% by weight. Since the polyimideobtained by the direct imidation using the catalytic system comprisingthe lactone and the base is obtained in the form of solution in whichthe polyimide is dissolved in the polar solvent, and since theconcentration of the polyimide in the obtained solution is within thepreferred range mentioned above, the polyimide solution produced by theabove-described process may advantageously be used as it is. If desired,however, the produced polyimide solution may be diluted with a diluent.As the diluent, a solvent which does not largely decrease thesolubility, such as dioxane, dioxolan, γ-butyrolactone, cyclohexanone,propylene glycol monomethyl ether acetate, methyl lactate, anisole,ethyl acetate or the like may be employed, although the diluent is notrestricted to these.

To make the composition of the present invention fitted to each finaluse, the sensitivity of the pattern resolution may be increased bygiving a photosensitizer to the photosensitive polyimide of the presentinvention. Although not restricted, examples of the photosensitizerinclude Michler's ketone, benzoin ether, 2-methylanthraquinone,benzophenone, benzoic acid esters and the like. Further, modifiers whichare added to the ordinary photosensitive polyimides, such as couplingagents, plasticizers, film-forming resins, surfactants, stabilizers,spectrum sensitivity-adjusters and the like may be added. In cases wherethe adhesion of the polyimide to the substrate is not good, by adding acoupling agent, especially a silane coupling agent such asγ-aminopropyltriethoxysilane, hexamethyldisiloxane,hexarnethyldisilazane or 1,3-bis(3-aminopropyl)tetramethyldisiloxane,the adhesion to the substrate may be improved, so that the polyimide canbe used as a photolithography material. In this case, the amount of thesilane coupling agent to be added may suitably be about 2 to 0.5% byweight.

By applying the photosensitive polyimide composition of the presentinvention in the form of solution on a substrate, drying thecomposition, selectively exposing the composition, and developing theresultant, a polyimide membrane having an arbitrary pattern on thesubstrate can be formed. Alternatively, by forming a polyimide film fromthe polyimide composition by a conventional method such as extrusion,adhering the film on a substrate, selectively exposing the film anddeveloping the resultant, a polyimide membrane having an arbitrarydesired pattern on the substrate may be formed. Since such a polyimidemembrane is resistant to heat and insulative, it may be used as aninsulation membrane or dielectric layer in semiconductor devices as itis. Alternatively, it may be used as a photoresist for selectivelyetching the substrate. In the present specification, in both cases wherethe polyimide is used as it is as an insulation film or dielectric layerin a semiconductor device or the like, and where the polyimide is usedas a photoresist for selective etching of the substrate, polyimide iscalled “photolithography material”. However, even in cases where thepatterned polyimide film after development is used as an insulation filmor a dielectric layer and not used for the selective etching of thesubstrate, the polyimide may also be called “photoresist” or “resist”for convenience.

Examples of the substrate to which the photosensitive polyimide of thepresent invention is applied include semiconductor disks, siliconwafers, germanium, gallium arsenide, glass, ceramics, copper foil,printed boards and the like.

Coating of the composition may be carried out usually by dipping,spraying, roll coating, spin coating or the like. As for the adhesivefilms, products having uniform thickness may be usually obtained byemploying thermocompression bonding.

A preferred mode for forming a pattern using the positive-typephotosensitive aliphatic/alicyclic polyimide according to the presentinvention will now be described.

A varnish containing the photoresist dissolved in the above-mentionedorganic solvent is applied on a prescribed substrate by roll coatingmethod, dipping method or the like, and then dried at a temperature ofnot higher than 150° C., preferably at 70 to 100° C. to form aphotoresist film. Examples of the substrate employed here includesilicon wafers, blank masks, and III-V group compound semiconductorwafers such as GaAs and AlGaAs. Alternatively, chromium- or chromiumoxide-deposited masks, aluminum-deposited substrates, IBPSG-coatedsubstrates, PSG-coated substrates, SOG-coated substrates, and carbonfilm sputter substrates may also be used. The thickness of the coatedfilm after drying is preferably about 0.2 μm to 200 μm.

Selective exposure to an actinic ray is carried out through a mask, orthe surface of the photosensitive polyimide film may also be directlyirradiated with an actinic ray. Examples of the actinic ray includevarious UVs such as i-line, h-line and g-line of low pressure mercurylamp, light from xenon lamp, and far ultraviolet rays such as excimerlaser beams from KrF, ArF or the like, X-ray, electron beam, gamma ray,neutron ray and ion beams. The advantageous effect of the presentinvention is maximally obtained when the exposure is carried out usingi-line, KrF excimer laser or ArF excimer laser, which has a shortwavelength. That is, the advantageous effect of the present invention ismaximally obtained when using a light having a wavelength of not morethan 365 nm, especially less than 250 nm (e.g., KrF and ArF excimerlaser). The dose of irradiation may be appropriately selected dependingon the photoabsorption rate by the polyimide, the type of the light, thetype of the pattern to be formed and the like, by conducting a routineexperiment, and when UV light is used, the dose of irradiation isusually about 100 to 3000 mJ/cm².

The photoresist film is then optionally heated (baked) at 50° C. to 150°C., preferably 60° C. to 120° C. by heating on a hot plate or in anoven, or by irradiation with infrared light. If the temperature of theheat treatment is lower than 50° C., the acid generated by the photoacidgenerator may not sufficiently react with the compound having thesubstituent groups decomposed by the acid. On the other hand, if thetemperature is higher than 150° C., the exposed area and the non-exposedarea of the photoresist film may be excessively decomposed orexcessively cured. By the above-mentioned baking, in the exposed area ofthe photoresist film, the acid generated by the exposure acts as acatalyst and reacts with the compound having substituent groups whichare decomposed by the acid. That is, the substituent groups on thecompound, which groups are decomposed by the acid, are decomposed sothat the compound is converted to an alkali-soluble compound. In somecases, by leaving the photoresist film at room temperature for a longtime, the same effect obtained by the above-mentioned post-baking may beobtained.

The photoresist film after baking is then subjected to development withan alkaline developer by immersion method or spray method to selectivelydissolving and removing the exposed areas of the photoresist film,thereby obtaining the desired pattern. Examples of the alkaline solutionused as the developer include inorganic aqueous alkaline solutions suchas aqueous solutions of sodium hydroxide, sodium carbonate and sodiummetasilicate, and organic aqueous alkaline solutions such as aqueoussolutions of tetramethylammonium hydroxide, trimethylhydroxyammoniumhydroxide and ethanolamine, as well as these aqueous solutions to whichone or more alcohols, surfactants or the like are added.

Since the photosensitive composition according to the present inventionhas very high solubility in alkali, the polyimide membrane pattern isfree from cracks and jagging, and the pattern is not collapsed. Further,the pattern can be formed with a high reproducibility. In addition, theobtained pattern has a very high resolution. Therefore, by using theresist pattern as an etching mask for dry etching, very fine patternwith a size of less than 1 μm can be accurately transcribed to theexposed substrate. One or more steps other than those mentioned abovemay be added without any problems. For example, a step of forming a flatlayer used as the bed layer of the photoresist film, a pre-treatmentstep for improving adhesiveness between the photoresist film and the bedlayer, a rinsing step for removing the developer with water or the likeafter development, a step of re-irradiation of UV before dry etchingand/or the like may be optionally carried out.

As described above, in the photosensitive composition according to thepresent invention, since (an) aliphatic or alicyclic compound(s),especially (an) alicyclic compound(s) is(are) incorporated in the mainchain of the polymer, resistance to dry etching was drastically improvedwithout deteriorating the transparency. As the resins for formingresists, those containing benzene ring, such as cresol novolak andpolyhydroxystyrene are conventionally used. However, these resins havepoor transparency to UVs having extremely short wavelengths.

Since (an) aliphatic or alicyclic compound(s), especially (an) alicycliccompound(s) is(are) incorporated in the main chain of the polyimide,both the transparency to the UVs having extremely short wavelengths andthe resistance to dry etching are simultaneously satisfied.

A further advantage of using the block copolymer polyimide compound isthat the solubility in alkalis of the area of the resist in which themolecular chains are cleaved by the photoacid generator is increased byintroducing (an) ether bond(s), amine bond(s) and/or disulfide bond(s),so that the resolution of the resist is further improved.

Thus, by forming a resist film on a substrate by applying thephotosensitive composition according to the present invention on asubstrate, irradiation of actinic ray (exposure), heating (baking) andby development with an alkali, fine resist pattern with good patternprofile can be formed. In turn, by conducting dry etching on thesubstrate using the resist pattern as a mask, the pattern can beaccurately transcribed to the substrate without sagging or the like ofthe pattern.

After the selective exposure, the irradiated regions of the photoresistlayer may be removed by treating the photoresist layer with an alkalineaqueous solution as a developing solution. The treatment may be carriedout by, for example, dipping the photoresist layer or spraying thedeveloper under pressure to the photoresist layer so as to dissolve theexposed regions thereof.

The development time varies depending on the energy of exposure,strength of the developer, manner of development, preheatingtemperature, temperature of the treatment with the developer and thelike. Usually, with the development by dipping, the development time isabout 1 to 10 minutes, and with the development by spraying, thedevelopment time is usually about 10 to 40 seconds. The development isstopped by, for example, dipping the developed layer in an inactivesolvent such as isopropanol or deionized water, or by spraying such asolvent.

By using the positive-type photosensitive polyimide compositionaccording to the present invention, polyimide coating layers having alayer thickness of 0.2 to 50 μm, and relief structures having sharpedges may be formed.

Since the polyimide in the composition of the present invention iscomposed of complete linear polyimide, it is not changed in water orheating, and its storage stability is good. Therefore, it can be used asphotosensitive films. Further, after forming the pattern by development,unlike the polyamic acid molecules, the postbake at 250 to 450° C. isnot necessary, and only drying under heat at 120 to 200° C. to evaporatethe solvent is carried out. Further, the polyimide membrane afterforming the pattern is tough, resistant to high temperature andexcellent in mechanical properties.

The resolution and photosensitivity, as well as the heat resistance,chemical resistance and mechanical strength, of the positive-typephotosensitive polyimide, are variable depending on the molecular weightand the molecular weight distribution. There is a tendency that thelarger the molecular weight and the smaller the imide group content, thelonger the development time and the dipping time in the alkali solution.As for heat resistance, chemical resistance and mechanical strength,polyimides having average molecular weights in terms of polystyrene of5000 to 100,000, preferably 10,000 to 50,000 give good results.

The above-described polyimide, when selectively exposed with an actinicray such as electron beam, shows negative-type photosensitivity. Apreferred mode of the method for forming a pattern with negative-typephotosensitivity will now be described.

A varnish containing the photoresist dissolved in the above-mentionedorganic solvent is applied on a prescribed substrate by roll coatingmethod, dipping method or the like, and then dried at a temperature ofnot higher than 150° C., preferably at 80 to 120° C. to form aphotoresist film. Examples of the substrate employed here includesilicon wafers, blank masks, and III-V group compound semiconductorwafers such as GaAs and AlGaAs. Alternatively, chromium- or chromiumoxide-deposited masks, aluminum-deposited substrates, IBPSG-coatedsubstrates, PSG-coated substrates, SOG-coated substrates, and carbonfilm sputter substrates may also be used. The thickness of the coatedfilm after drying is preferably about 0.2 μm to 200 μm.

Selective exposure to an actinic ray is carried out through a mask, orthe surface of the photosensitive polyimide layer may also be directlyirradiated with an actinic ray. Examples of the actinic ray includeX-ray, electron beam, gamma ray, neutron ray and ion beams. Theadvantageous effect of the resist composition according to the presentinvention is maximally obtained when the exposure is carried out usingelectron beam. The dose of irradiation may be appropriately selecteddepending on the absorption rate of the electron beam by the polyimide,the type of the pattern to be formed and the like, by conducting aroutine experiment, and the dose of irradiation is usually about 1μC/cm² to 1000 μC/cm².

The photoresist film is then optionally heated (baked) at 80° C. to 150°C., preferably 80° C. to 120° C. by heating on a hot plate or in anoven, or by irradiation with infrared light. Then a required dose ofelectron beam is irradiated.

Then the photoresist film is subjected to development with an alkalinedeveloper by immersion method to selectively dissolving and removing thenon-exposed areas of the photoresist film, thereby obtaining the desiredpattern. Examples of the alkaline solution used as the developer includeinorganic aqueous alkaline solution such as aqueous solutions of sodiumhydroxide, sodium carbonate and sodium metasilicate, and organic aqueousalkaline solutions such as aqueous solutions of tetramethylammoniumhydroxide, trimethylhydroxyammonium hydroxide and ethanolamine, as wellas these aqueous solutions to which one or more alcohols, surfactants orthe like are added.

Since the aliphatic/alicyclic polyimide composition according to thepresent invention has very high solubility in alkali, the polyimidemembrane pattern is free from cracks and jagging, and the pattern is notcollapsed. Further, the pattern can be formed with a highreproducibility. In addition, the obtained pattern has a very highresolution. Therefore, by using the resist pattern as an etching maskfor dry etching, very fine pattern with a size of less than 1 μm can beaccurately transcribed to the exposed substrate. One or more steps otherthan mentioned above may be added without any problems. For example, astep of forming a flat layer used as the bed layer of the photoresistfilm, a pre-treatment step for improving adhesiveness between thephotoresist film and the bed layer, a rinsing step for removing thedeveloper with water or the like after development, a step ofre-irradiation of UV before dry etching and/or the like may beoptionally carried out.

Since (an) aliphatic or alicyclic compound(s), especially (an) alicycliccompound(s) is(are) incorporated in the main chain of thealiphatic/alicyclic polyimide of the present invention, both thetransparency to the lights having extremely short wavelengths and theresistance to dry etching are simultaneously satisfied.

A further advantage of using the block copolymer polyimide compound isthat by introducing (an) ether bond(s), amine bond(s) and/or disulfidebond(s), intermolecular crosslinking reaction occurs by irradiation withelectron beam, so that the solubility in alkalis of the exposed area ofthe resist is decreased and the resolution of the resist is furtherimproved.

Thus, by forming a resist film on a substrate by applying thephotosensitive composition according to the present invention on asubstrate, irradiation of electron beam (exposure), heating (baking) andby development with an alkali, fine resist pattern with good patternprofile can be formed. In turn, by conducting dry etching on thesubstrate using the resist pattern as a mask, the pattern can beaccurately transcribed to the substrate without sagging or the like ofthe pattern. After the selective exposure, the non-irradiated regions ofthe photoresist layer may be removed by treating the photoresist layerwith an alkaline aqueous solution as a developing solution. Thetreatment may be carried out by, for example, dipping the photoresistlayer so as to dissolve the non-exposed regions thereof.

The development time varies depending on the energy of exposure,strength of the developer, manner of development, preheatingtemperature, temperature of the treatment with the developer and thelike. Usually, with the development by dipping, the development time ispreferably 30 seconds to 4 minutes. The development may be stopped by,for example, dipping the developed layer in an inactive solvent such asisopropanol or deionized water, or by spraying such a solvent.

By using the negative-type aliphatic/alicyclic polyimide employed in thepresent invention, polyimide coating layers having a layer thickness of0.05 to 1 μm, and relief structures having sharp edges may be formed.

Since the aliphatic/alicyclic polyimide in the composition of thepresent invention is composed of complete linear polyimide, it is notchanged in water or heating, and its storage stability is good.Therefore, it can be used as photosensitive films. Further, afterforming the pattern by development, unlike the polyamic acid molecules,the postbake at 250 to 450° C. is not necessary, and only drying underheat at 120 to 200° C. to evaporate the solvent is carried out. Further,the polyimide membrane after forming the pattern is tough, resistant tohigh temperature and excellent in mechanical properties.

The resolution and photosensitivity, as well as the heat resistance,chemical resistance and mechanical strength, of the negative-typephotosensitive polyimide, are variable depending on the molecular weightand the molecular weight distribution, as in the positive-typephotosensitive polyimide.

The present invention will now be described in more detail by way ofexamples thereof.

Since characteristic photosensitive polyimides are obtained by variouscombinations of acid dianhydrides and aromatic diamines, the presentinvention is not restricted to these examples.

REFERENCE EXAMPLE 1

A stainless steel anchor agitator and reflux condenser were attached toa 500 ml three-necked separable flask, the condenser comprising a trapand a cooling tube having balls and mounted on the trap.

To this flask, 26.27 g (0.125 mol) of cyclopentanetetracarboxylicdianhydride (commercial product of Aldrich), 6.21 g (0.025 mol) of1,3-bis(3-aminopropyl)tetramethyldisiloxane (commercial product ofShin-etsu Chemical Co., Ltd., molecular weight: 248.5), 1.3 g (0.0 13mol) of δ-valerolactone, 2.1 g (0.026 mol) of pyridine, 150 g ofγ-butyrolactone and 50 g of toluene were added.

After stirring the mixture at 180 rpm at room temperature under nitrogenatmosphere for 0.5 hours, 17.72 g (0.05 mol) of3,4-bis(3-aminopropyl)-2,4,8,10-tetraoxaspiro{5,5}undecane (commercialproduct of Tokyo Chemical Industry Co., Ltd.), 10.02 g (0.05 mol) of1,4-bis(3-aminopropyl)piperazine (commercial product of Tokyo ChemicalIndustry Co., Ltd.), 100 g of γ-butyrolactone and 50 g of toluene wereadded. After stirring the mixture at room temperature for 1 hour, themixture was heated at 180° C. and stirred at 180 rpm for 4 hours and 5minutes. During the reaction, toluene-water azeotrope was removed.

The polymer concentration of the polyimide solution thus obtained was20% by weight. The molecular weight of this polyimide was measured byhigh performance liquid chromatography (commercial product of TosohCorporation). The molecular weights based on polystyrene were: MostFrequent Molecular Weight (M): 24,700; Number Average Molecular Weight(Mn): 17,900; Weight Average Molecular Weight (Mw): 37,800; Z AverageMolecular Weight (Mz): 93,400; Mw/Mn=2.11; Mz/Mn=4.67. Thecharacteristics of this aliphatic polyimide copolymer (19-53) are shownin Tables 1-1 and 1-2.

REFERENCE EXAMPLE 2

Operations were carried out as in Reference Example 2.

To the flask, 52.85 g (0.2 mol) of5(2,5-dioxo-tetrahydrofurfuryl)-3-methyl-3-cyclohexene-1,2-dicarboxylicanhydride (commercial product of Tokyo Chemical Industry Co., Ltd.),12.43 g (0.05 mol) of 1,3-bis(3-aminopropyl)tetramethyldisiloxane(molecular weight: 248.5), 7.26 g (0.05 mol) ofN,N-bis(3-aminopropyl)methylamine (commercial product of Tokyo ChemicalIndustry Co., Ltd.), 2.0 g (0.02 mol) of 8-valerolactone, 3.2 g (0.04mol) of pyridine, g of γ-butyrolactone and 70 g of toluene were added.

After stirring the mixture at 180 rpm at room temperature under nitrogenatmosphere for 1 hour, 27.44 g (0.10 mol) of3,4-bis(3-aminopropyl)-2,4,8,10-tetraoxaspiro {5,5} undecane (commercialproduct of Tokyo Chemical Industry Co., Ltd.), 128 g of γ-butyrolactoneand 30 g of toluene were added. After stirring the mixture at roomtemperature for 1 hour, the mixture was heated at 180° C. and stirred at180 rpm for 3 hours and 5 minutes. During the reaction, toluene-waterazeotrope was removed.

The polymer concentration of the polyimide solution thus obtained was20% by weight. The molecular weight of this polyimide was measured byhigh performance liquid chromatography (commercial product of TosohCorporation). The weight average molecular weight (Mw) in terms ofpolystyrene was 73920. The characteristics of this aliphatic polyimidecopolymer (19-56) are shown in Tables 1-1and 1-2.

REFERENCE EXAMPLE 3-REFERENCE EXAMPLE 7

The operations as in Reference Example 1 were repeated except that thetype of the acid dianhydride and the diamine constituting the polyimidecopolymer were changed. The reaction time of the second step inReference Example 1 is shown in Table 1.

TABLE 1-1 Synthesis Reaction of Various Aliphatic Polyimide CopolymersComposition of Materials Reaction Polyimide Reference Synthesis ofSynthesis Time of Concentration/ Examples No. Reaction Second StepSolvent Reference 19-53 (3.5 Cp + 0.5 4′05″ 20%/Lc Example 1 SiP) (Spi +Pip) Reference 19-56 (2.0 Ma + 0.5 3′05″ 20%/Lc Example 2 SiM + 0.5 Am)(Spi) Reference 19-48 (2.5 Ma + 0.5 3′20″ 20%/Lc Example 3 SiP) (Spi +Pip) Reference 19-26 (2 PMD + 1 Si) 4′00″ 20%/NMP Example 4 (2 Ma + SS +2 Spi) Reference 18-201 (2 Cp + 1 Ch) 4′40″ 20%/NMP Example 5 (Phss)Reference 19-12 (2 Cp + 1 Ch) 3′00″ 20%/NMP Example 6 (ss) Reference19-45 (2.5 BCD + 0.5 2′00″ 20%/NMP Example 7 SiP) (Spi + Dicy)

TABLE 1-2 Molecular Characteristics and Absorption Rate of UV of VariousAliphatic Polyimide Copolymers Absorption Polyimide Molecule Rate (%) ofReference Synthesis Including Adhesion to Double Benzene WavelengthExamples No. of Si Substrate bond Ring 248 nm Reference 19-53 yes yes 00 34 Example 1 Reference 19-56 yes yes 4 0 98 Example 2 Reference 19-48yes yes 5 0 98 Example 3 Reference 19-26 yes yes 4 2 68 Example 4Reference 18-201 no no 0 2 n.d. Example 5 Reference 19-12 no no 0 0 n.d.Example 6 Reference 19-45 yes no 2.5 0 n.d. Example 7 n.d.: notdetermined

EXPLANATION OF TABLE 1-1

Synthesis Reaction, Composition of Materials: The upper line indicatesthe composition of the materials in the reaction of the first step, andthe lower line indicates the composition of the materials in thereaction of the second step. (Explanation of Symbols in the Tables) (Thenumbers in front of the symbols in the tables indicate the number ofmoles of the material).

Cp: cis-1,2,3,4-cyclopentanetetracarboxylic dianhydride

SiP: 1,3-bis(3-aminopropyl)tetramethyldisiloxane

Spi: 3,4-bis(3-aminopropyl)-2,4,8,10-tetraoxaspiro {5,5}undecane

Pip: 1,4-bis(3-aminopropyl)piperazine

Ma:5(2,5-dioxo-tetrahydrofurfuryl)-3-methyl-3-cyclohexene-1,2-dicarboxylicanhydride

SiM: 1,3-bis(3-aminopropyl)tetramethyldisiloxane

PMD: pyromellitic dianhydride

Si: diaminosiloxane (average amine value: 421)

SS: 2,2′-diamininoethyldisulfide

Am: N,N-bis(3-aminopropyl)methylamine

Ch: 1,3-bis(aminomethyl)cyclohexane

Phss: bis(4-aminophenyl)disulfide

ss: 2,2′-diaminodiethyldisulfide

BCD: bicyclo(2,2,2)-oct-7-ene-2,3,5,6-tetracarboxylic dianhydride

Dicy: 4,4′-diamino-dicyclohexylmethane

Reaction Time of Second Step in Reference Example 1

4 hours and 5 minutes (4′05″): hereinafter described in the same manner

Polyimide Concentration/Solvent: Polyimide concentration is expressed interms of % by weight in the solvent.

Lc: butyrolactone

NMP: N-methylpyrrolidone

EXPLANATION OF TABLE 1-2

Including of Si: Whether the aliphatic polyimide copolymer moleculecontains

Si element or not

Adhesion to Substrate: Aliphatic polyimide copolymer was applied on asilicon wafer substrate by spin-coating method, and the adhesion of thealiphatic polyimide copolymer was evaluated by cross cut test (peelingoff of lattices of 1 mm, 10×10 is not observed in adhesion test)

Absorption Rate of 248 nm: Photoabsorption of the polyimide solution wasmeasured. Aliphatic polyimide copolymer having no double bond issubjected to experiment.

All of the polyimides described in References 1 to 7 can be used as thematerials for photolithography. Although the polyimides obtained inReference Examples 5 to 7 have poor adhesion to the substrate, they maybe used as the materials for photolithography by blending a silanecoupling agent as mentioned above. Although the polyimide obtained inReference. Examples 2 and 3 have large absorption rates of KrF (248 nm)line, photolithography can be attained by using KrF line by increasingthe dose of irradiation, or by using a light having a longer wavelength,photolithography can be attained with a normal dose of radiation.

EXAMPLE 1

(A) Process of Producing 2,2′-diaminodiethyl disulfide

In one-liter beaker, 100 g of cystamine, 44.2 g of potassium hydroxideand 440 g of isopropylalcohol were placed, and the mixture is stirredover one day and night with a magnetic stirrer. The solution wasfiltered and concentrated by a rotary evaporator at 60° C. to obtain 48g (yield 72%) of 2,2′-diaminodiethyl disulfide.

(B) The operations as in Reference Example 1 were repeated.

To the flask, 19.86 g (0.08 mol) of BCD, 33.68 g (0.04 mol) ofdiaminosiloxane (amine value: 421), 1.6 g (0.016 mol) ofδ-valerolactone, 2.6 g (0.032 mol) of pyridine, 200 g ofN-methylpyrrolidone and 100 g of toluene were added.

After stirring the mixture at 180 rpm at room temperature under nitrogenatmosphere for 1 hour, the mixture was heated at 180° C. and stirred at180 rpm for 1 hour. During the reaction, toluene-water azeotrope wasremoved.

After cooling the mixture to room temperature, 16.8 g (0.08 mol) ofcyclopentanetetracarboxylic dianhydride, 6.1 g (0.04 mol) of2,2′-diaminodiethyldisulfide, 11.38 g (0.08 mol) of1,3-bis(aminomethyl)cyclohexane, 128 g of γ-butyrolactone and 30 g oftoluene were added. After stirring the mixture at 180 rpm at roomtemperature under nitrogen atmosphere for 1 hour, the mixture was heatedat 180° C. and stirred at 180 rpm for 2 hours. During the reaction,toluene-water azeotrope was removed.

The polymer concentration of the polyimide solution thus obtained was20% by weight. The molecular weight of this polyimide was measured byhigh performance liquid chromatography (commercial product of TosohCorporation). The molecular weights based on polystyrene were: NumberAverage Molecular Weight (Mn): 9000; Weight Average Molecular Weight(Mw): 10,700; Z Average Molecular Weight (Mz): 13,000.

(C) The same operations as in above-described (B) were carried outexcept that the reaction in the second step was carried out for 3 hours.The polymer concentration of the polyimide solution thus obtained was20% by weight. The molecular weight of this polyimide was measured byhigh performance liquid chromatography (commercial product of TosohCorporation). The molecular weights based on polystyrene were: NumberAverage Molecular Weight (Mn): 12,300; Weight Average Molecular Weight(Mw): 17,400; Z Average Molecular Weight (Mz): 25,000.

(D) To 110 g of the polyimide solution obtained in (C), 50 g of methanolwas added and the mixture was stirred. To the mixture, 50 g of water wasadded dividedly in three times. The generated precipitates wereseparated by decantation, and 50 g of methanol, and then 100 g of waterwere added thereto. The mixture was heated to 60° C. and stirred,followed by decantation. To the obtained product, 50 ml of methanol wasadded and the mixture was heated to 60° C., followed by stirring,leaving to stand and then decantation. To the obtained product, 100 g ofdioxolan was added to dissolve the precipitates, and the resultingsolution was filtered through a 0.8 μm pore filter, followed byconcentration and evaporation to dryness by a rotary evaporator. Theproduct was dried in vacuum at 1 mmHg at 110° C. to obtain powder. Thepowder was dissolved in dimethylformamide and subjected to highperformance liquid chromatography (commercial product of TosohCorporation). The molecular weights based on polystyrene were: NumberAverage Molecular Weight (Mn): 15,000; Weight Average Molecular Weight(Mw): 20,000; Z Average Molecular Weight (Mz): 27,600. Decomposition ofthis compound started at 387° C.

EXAMPLE 2 Method for Forming Images

(A) One gram of the polyimide powder obtained in Example 1(D), 19 g ofdioxolan and 0.2 g of a photosensitizer (NT-200: triester between2,3,4-trihydroxybenzophenone and6-diazo-5,6-dihydro-5-oxo-naphthalene-1-sulfonic acid (commercialproduct of Toyo Gosei Co., Ltd.) were mixed and dissolved. The solutionwas filtered through a 0.2 μm pore filter and the obtained polyimidesolution was applied on the surface of a silicon wafer substrate byspin-coating method. After coating the solution at 500 rpm for 5 secondsand at 5000 rpm for 30 seconds, the resulting substrate was prebaked inan infrared dryer at 90° C. for 10 minutes. The thickness of thispolyimide film was 0.4 μm.

On this photoresist coating layer, a test pattern for positive-typephotomask was placed, and the photoresist was irradiated by a mercurylamp i-line irradiation apparatus at a dose of 200 mJ/cm². Thisphotosensitive photoresist film was developed with 0.05% aqueoussolution of tetramethylammonium hydroxide (TMAH) for 19 seconds, andthen dried by an infrared dryer at 150° C. for 10 minutes, followed byobservation of the resulting pattern image with an electron microscopy.A sharp image of the line-and-space image of 0.35 μm was observed.

(B) Water was added to the positive-type polyimide solution obtained inExample 1(B) to precipitate the polyimide and the precipitates wererecovered by filtration, followed by drying the precipitates underreduced pressure of 1 mmHg at 110° C. to obtain dry powder.

To 1 g of the thus obtained polyimide powder, 9 g of dioxolan and 0.2 gof NT-200 were added, and the mixture was filtered through a 0.2 μm finepore filter. The resulting composition was applied on a silicon wafer asin (A) to obtain a photosensitive polyimide film having a thickness of0.52 μm.

On this photoresist coating layer, a test pattern for positive-typephotomask was placed, and the photoresist was irradiated by a mercurylamp i-line irradiation apparatus at a dose of 1800 mJ/cm². Thisphotosensitive photoresist film was developed with 0.05% aqueoussolution of tetramethylammonium hydroxide for 2 minutes and 20 seconds,and then dried by an infrared dryer at 150° C. for 10 minutes, followedby observation of the resulting pattern image with an electronmicroscopy. A sharp image of the line-and-space image of 0.40 μm wasobserved. However, with the image of 0.4 μm, photoresist was left overin the space regions and the boundaries were not clear. It is presumedthat this photoresist film contained polyamic acid in addition topolyimide.

EXAMPLE 3

The operations as in Example 2 were repeated except that a KrF(wavelength 248 nm) irradiator was used as the light source, the dose ofirradiation was 170 mJ/cm², and that the development was carried outusing 0.05% TMAH for 20 seconds.

As a result, a sharp line-and-space pattern with a width of 0.16 μm wasformed.

EXAMPLE 4

Resoluting Speed of Various Aliphatic/Alicyclic Polyimide Copolymers

To 2 g of each of various aliphatic/alicyclic polyimide copolymers, 8 gof a solvent (dioxolan or N-methylpyrrolidone) was added to dissolve thepolyimide, and the obtained polyimide solution was filtered through a0.8 μm fine pore filter, followed by addition of 0.2 g of NT-200 toobtain a photosensitive polyimide solution.

The photoresist composition was applied on the surface of asurface-treated copper foil having a diameter of 5 cm (commercialproduct of Mitsui Metal and Mining Co., Ltd.: thickness 18 μm), anddried by an infrared dryer at 90° C. for 10 minutes. The thickness ofthe photoresist film was about 10 μm. On this photosensitive film, atest pattern (10, 15, 20, . . . , 50 μm, respectively) was placed, andthe photosensitive film was irradiated at a dose of exposure at whichimages are obtained using 2 kW extra-high pressure mercury lampapparatus (JP-2000G, commercial product of Oak Seisakusho). Thedevelopment was carried out using varying concentrations of aqueoustetramethylammonium hydroxide (TMAH) as a developing solution in anultrasonic washer. The resolution of 15 μm was sharp and the resolutionof 10 μm was confirmed. The material composition and the patterningconditions of each polyimide are shown in Table 2. The polyimideobtained in Example 8(D) was also subjected to the patterning usingmercury g-line, and the results are also shown in Table 2.

TABLE 2 Resolution Test of Various Aliphatic Polyimide CopolymersMaterial Dose of TMAH Development Synthesis Composition of RadiationConcentration Time Examples No. Synthesis Reaction mJ/cm² (%) (min/sec)Example 1 19-161 Described in 500 0.01 1′30″ Example 1 Example 4-116-118 (2.0 Ma + Pip + Ch) 500 2 3′30″ Example 4-2 16-120 (2 BCD + Pip +Ch) 500 10 1′20″ Example 4-3 19-99 (2 Cp + Am + Ch) 1000 0.01   52″Example 4-4 19-110 (2 Cp + Oxy + Ch) 1000 0.05   30″

EXAMPLE 5

Each of the polyimides described in Examples 4-1to 4-4 was exposed tomercury i-line and patterned as in Example 2. As a result, sharpline-and-space pattern having a width of 0.4 μm was formed.

The conditions of the step of forming the images are shown in Table 3below.

TABLE 3 Material Dose of TMAH Development Synthesis Composition ofRadiation Concentration Time Examples No. Synthesis Reaction mJ/cm² (%)(min/sec) Example 4-1 16-118 (2.0 Ma + Pip + Ch) 1800 3.0 4′30″ Example4-2 16-120 (2 BCD + Pip + Ch) 1800 10 6′00″ Example 4-3 19-99 (2 Cp +Am + Ch) 3000 0.05 1′30″ Example 4-4 19-110 (2 Cp + Oxy + Ch) 3600 0.11′30″

EXAMPLE 6 Method for Forming Images With Electron Beam

To 2 g of the polyimide powder obtained in Example 1(D), 18 g ofdioxolan was added and the resultant was mixed with a mixer to dissolvethe polyimide, thereby obtaining 10% by weight aliphatic polyimidesolution, followed by filtering the solution through a 0.2 μm fine porefilter. The polyimide solution was applied on the surface of a siliconwafer substrate by the spin-coating method and the substrate was heatedon a hot plate at 100° C. for 30 minutes, at 120° C. for 30 minutes, andat 150° C. for 30 minutes. The thickness of this polyimide film was 1.0μm.

On this photoresist coating film, a test pattern for negative-typephotomask was placed, and the photoresist was irradiated by ELIONIX-5000electron beam irradiator at an acceleration voltage of 20 kV, beamdiameter of 0.3 μm, and at a beam current of 800 pA. The dose ofirradiation of the electron beam was within the range of 10 μC/cm² to1000 μC/cm². The best dose of irradiation of electron beam was 60μC/cm², and negative-type pattern was obtained. The photoresist film wasdeveloped with 0.25% aqueous tetramethylammoniumhydroxide solution for10 seconds to 1 minute, and then washed with ion-exchanged water. Afterdrying the photoresist at 150° C. for 10 minutes by an infrared dryer,the negative-type pattern image was observed with an electronmicroscope. A sharp image of line-and-space pattern having a width of0.35 μm and a thickness of 1 μm was observed.

EXAMPLE 7 Method for Forming Images with Electron Beam

Operations were carried out as in Example 6.

To the polyimide powder obtained in Example 1(D), dioxolan was added andthe resultant was mixed with a mixer to dissolve the polyimide, therebyobtaining 7.5% by weight aliphatic polyimide solution, followed byfiltering the solution through a 0.2 μm fine pore filter. The polyimidesolution was applied on the surface of a silicon wafer substrate by thespin-coating method and the substrate was heated on a hot plate at 100°C. for 30 minutes. The thickness of this polyimide film was 200 nm.

On this photoresist coating film, a test pattern for negative-typephotomask was placed, and the photoresist was irradiated by ELIONIX-5000electron beam irradiator at an acceleration voltage of 20 kV, beamdiameter of 0.3 μm, and at a beam current of 300 pA. The dose ofirradiation of the electron beam was 2.4 μC/cm² and negative-typepattern was obtained. The photoresist film was developed with 0.25%aqueous tetramethylammoniumhydroxide solution and then washed withion-exchanged water. After drying the photoresist at 150° C. for 10minutes by an infrared dryer, the negative-type pattern image wasobserved with an electron microscope. A sharp image of line-and-spacepattern having a width of 100 nm and a thickness of 200 nm was observed.

EXAMPLE 8 Investigation of Resistance to Dry Etching

(A) To the polyimide powder obtained in Example 1(D), dioxolan was addedand the resultant was mixed with a mixer to dissolve the polyimide,thereby obtaining 10% by weight aliphatic polyimide solution, followedby filtering the solution through a 0.2 μm fine pore filter. Thepolyimide solution was applied on the surface of a silicon wafersubstrate by the spin-coating method and the substrate was heated on ahot plate at 100° C. for 30 minutes, at 120° C. for 30 minutes, and at150° C. for 30 minutes. The thickness of this polyimide film was 325 nm.

This photoresist coating film was subjected to etching treatment usingDEM451 T from ANELVA. On the other hand, the polyimide photoresistmaterial which was not irradiated with electron beam was subjected tothe following test for resistance to etching gas. Etching gas: SF6; GasFlow Rate: 60 sccm; Dose: 80W; Time: 10 minutes. The etching rate wasmeasured. The etching rate of Si was 0.27 μm/min., that of AZ resist was34 nm/min, and that of the aliphatic polyimide was 1.7 nm/min. Thus, thealiphatic polyimide photoresist showed high resistance to dry etching.

(B) To the polyimide powder obtained in Example 1(D), dioxolan was addedand the resultant was mixed with a mixer to dissolve the polyimide,thereby obtaining an aliphatic polyimide solution, followed by filteringthe solution through a 0.2 μm fine pore filter. The polyimide solutionwas applied on the surface of a silicon wafer substrate by thespin-coating method and the substrate was heated on a hot plate at 100°C. for 30 minutes, at 120° C. for 30 minutes, and at 150° C. for 30minutes. The thickness of this polyimide film was 412 nm.

This photoresist coating film was subjected to etching treatment usingDEM45 IT from ANELVA. On the other hand, the polyimide photoresistmaterial which was not irradiated with electron beam was subjected tothe following test for resistance to etching gas. Etching gas: SF6; GasFlow Rate: 60 sccm; Dose: 300W; Time: 10 minutes. After the etchingtreatment with the reactive ions, the regions irradiated with theelectron beam was cured, and this selectivity was 150 times with respectto Si.

What is claimed is:
 1. A positive-type photosensitive polyimidecomposition comprising a solvent-soluble polyimide which showspositive-type photosensitivity in the presence of a photoacid generator,which is obtained by polycondensation of at least one aliphatictetracarboxylic dianhydride and/or alicyclic tetracarboxylic dianhydrideand at least one aliphatic diarnine and/or alicyclic diamine and/ordiaminosiloxane; and said photoacid generator.
 2. The polyimidecomposition according to claim 1, wherein the moiety in said aliphaticdiamine and/or alicyclic diamine and/or diaminosiloxane, which moietyconstitutes the main chain of said polyimide, consists essentially ofC₁-C₁₅ saturated aliphatic structure and/or C₃-C₁₅ saturated alicyclicstructure.
 3. The composition according to claim 2, wherein saidtetracarboxylic dianhydride is a saturated alicyclic tetracarboxylicdianhydride and/or bicyclo(2,2,2)-oct-7-ene-2,3,5,6-tetracarboxylicdianhydride and/or5-(2,5-dioxo-tetrafirfuryl)-3-methyl-4-cyclohexene-1,2-dicarboxylicanhydride.
 4. The composition according to claim 3, wherein saidsaturated alicyclic tetracarboxylic dianhydride comprises acyclopentanetetracarboxylic dianhydride, and/orcyclohexanetetracarboxylic dianhydride and/or cyclobutanetetracarboxylicdianhydride.
 5. The composition according to claim 1, which is apolyimide copolymer comprising two or more diamines selected from thegroup consisting of 1,3-bis(3-aminomethyl)cyclohexane,4,4′-diamino-dicyclohexyl-methane, bis(2-aminoethoxy)ethane,N,N-bis(3-aminopropyl)methylamine, ethylenediamine,2,2′-diaminodiethyldisulfide, 1,4-bis(3-aminopropyl)piperazine,3,4-bis(3-aminopropyl)2,4,8,10-tetraoxa[5,5]undecane, diaminosiloxane,trans-1,4-diaminocyclohexane, 1,3-diamino-2-hydroxypropane, and3(4),8(9)-bis(aminoethyl)tricyclo{5,2,1,0 } decane.
 6. The compositionaccording to claim 5, wherein said diamine has disulfide structureand/or diaminosiloxane in the moiety constituting the main chain.
 7. Thecomposition according to any one of claims 1-6, wherein said polyimideis a polyimide block copolymer obtained by polycondensing saidtetracarboxylic dianhydride and said diamine in a solution in thepresence of an acid catalyst.
 8. The composition according to claim 7,wherein said acid catalyst is a composite catalyst consistingessentially of valerolactone and pyridine or methylmorpholine, and saidpolyimide block copolymer is one obtained by first polycondensing saidtetracarboxylic dianhydride and said diamine in a solution, and thenanother tetracarboxylic dianhydride and/or diamine is(are) added forpolycondensation to attain a final molar ratio of the tetracarboxylicdianhydride(s) to the diamine(s) in said block copolymer of1:(0.95-1.05).
 9. The composition according to claim 1, wherein saidpolyimide has an average molecular weight in terms of polystyrene of5000 to 100,000.
 10. The composition according to claim 1, wherein saidpolyimide does not substantially comprise conjugated double bond andaromatic structure.
 11. A method for forming polyimide patterncomprising irradiating said polyimide recited in claim 1 with a light inthe presence of a photoacid generator, which polyimide is in the form ofa thin film coating a substrate; and removing the irradiated regionswith an alkaline developing solution.
 12. The method according to claim11, wherein a far-ultraviolet ray with a wavelength of not more than 365nm is employed as said light.
 13. The method according to claim 12,wherein a light beam with a wavelength of not more than 250 nm isemployed as said light.
 14. A method for forming a pattern ofpositive-type photosensitive polyimide comprising the steps of forming aphotosensitive layer consisting essentially of said polyimidecomposition according to claim 1 on a substrate; selectively irradiatingsaid photosensitive layer with a light beam having a wavelength of notmore than 365 nm; heat-treating said photosensitive layer; anddeveloping said photosensitive layer after said heat-treatment toselectively remove prescribed regions in said photosensitive layer. 15.Use of said polyimide recited in claim 1 as a material for positive-typephotolithography.
 16. A method for forming negative-type pattern ofpolyimide comprising coating a substrate with the polyimide recited inclaim 1; selectively irradiating the polyimide with an actinic ray, theirradiated regions constituting a desired pattern; and developing theirradiated polyimide with an alkaline solution to dissolve thenon-irradiated regions.
 17. The method according to claim 16, whereinsaid actinic ray is electron beam.
 18. Use of the polyimide recited inclaim 1 as a material for negative-type photolithography.